If you wish to accomplish auto repairs for your Hyosung RT125D then it is usually recommended to have access to a Workshop Manual to keep just for reference in case you want to know methods to remove a certain part for example the Gearbox and match it again accordingly.
Hyosung RT125D Workshop Manuals gives you specified diagnostic guides for your automobile therefore if something is wrong it helps you figure out what the issue is and ways to fix it. You will be able to evaluate if this can be done by yourself or if the job is too big you could make a booking for your RT125D right into a suitable friendly mechanic.
Hyosung RT125D manual